This article provides an understanding of orthodontic movement terminology and their associated complexity. It will greatly assist you in when discussing your patient’s movement requirements with Proligner when customising treatments, as well as enabling your understanding of Proligner’s orthodontic articles and education.
Orthodontic tooth movements can be broadly graded by complexity:
Facial-lingual movements Simple
Root tipping Simple
Mesial-distal movements Moderate
Translation Moderate
Retraction (Lingualisation) Moderate
Mesialisation (Protraction) Moderate
Distalisation Moderate
Most rotations Moderate
Intrusions (anterior) Moderate
Torqueing Difficult
Rotation (posterior) Difficult
Intrusions (posterior) Difficult
Extrusions Difficult
Expansion / Constriction Difficult
Each movement can be further graded in complexity by the degree of movement required. Which will be considered individually. A simple to follow Movement Classification Guideline is available for you to download summarising all movements. This is useful to keep on hand.
When beginning clear aligner treatment, it is wise to build your capability by starting with simple movements before advancing to more complex movements. Difficult treatments can often be challenging to achieve with aligners alone and may require auxiliary treatments. Difficult movements should be held off from treating until you have developed sufficient skills to manage them.
While “Short clinical crowns” is not a movement, they are listed as they are a stand-alone category considered difficult to treat as there is very little surface area of the crown for the aligner to interact with and achieve movement of both the crown and the root.
Movements
Crown Tipping (Facial-lingual tipping)
This is where is crown is tipped facially or lingually with the centre of rotation (CRot) is at the apex of the root. This movement is often used for anterior teeth aesthetics and alignment.
Crown Tipping (Degrees) | Simple | Moderate | Difficult |
Anterior | 0 - 10 | 10 - 20 | > 20 |
Posterior | 0 - 10 | 10 - 20 | > 20 |
Tipped teeth are more difficult to move that teeth that are upright. If a tipped tooth needs to be moved mesial or distal, it is easiest to first add an engager and to upright the tipped tooth then to move it in the desired direction.
Crown Tipping (Mesial-distal tipping)
This is where is crown is tipped mesial or distal with the centre of rotation (CRot) is at the apex of the root. This movement is often used for anterior teeth aesthetics and alignment.
Root Tipping (Degrees) | Simple | Moderate | Difficult |
Anterior | 0 - 10 | 10 - 15 | > 15 |
Posterior | 0 - 10 | 10 - 15 | > 15 |
Root Tipping
Root tipping, otherwise known as tipping of the root, is the mesial or distal movement of the tooth with the CRot at the crown of the tooth. This is important for anterior alignment and aesthetic finishing.
Root Tipping (Degrees) | Simple | Moderate | Difficult |
Anterior | 0 - 10 | 10 - 15 | > 15 |
Posterior | 0 - 5 | 5 - 10 | > 10 |
Proclination
This typically involves moving a group of teeth. It is tipping the crown of anterior teeth facial or labial. It is often used to resolve crowding. Often crowded teeth will not move because they lack sufficient room to move. With crowded teeth it is often useful to create the space. Engagers and IPR is often required, and or surrounding teeth are required to be moved to make room before completing the movement of the crowded tooth.
Rotations
Turning a tooth mesial or distal along the axis of the tooth. Can be important for occlusion.
Rotations (Degrees) | Simple | Difficult | |
Incisors | 0 - 15 | 15 - 30 | > 30 |
Canines | 0 - 10 | 10 - 20 | > 20 |
Molar/Bicuspids | 0 - 10 | 10 - 15 | > 15 |
To rotate a tooth, often space needs to be created. Usually, space is created first then the tooth is rotated. Rotating posterior teeth is considered a difficult movement.
Translation
Moving the tooth bodily in the mesial or distal or labial or lingual direction without changing the orientation of the long axis of the tooth.
Translation | Simple | Moderate | Difficult |
Anterior/Posterior | 0 - 2mm | 2 - 4mm | > 4mm |
Retraction (Lingualisation)
This involves tipping crown of anterior teeth towards the lingual.
Lingualisation | Simple | Moderate | Difficult |
| 0 - 2mm | 2 - 3mm | > 3mm |
Mesialisation (Protraction)
This is translating a tooth along the occlusal plan toward the midline.
Protraction is the term often used to describe the translation of the posterior teeth forward, moving them mesial, along the occlusal plane towards the midline.
Mesialisation | Simple | Moderate | Difficult |
| 0 - 2mm | 2 - 4mm | > 4mm |
Distalisation
This is translating a tooth along the occlusal plan away from the midline (towards the posterior).
Distalisation | Simple | Moderate | Difficult |
| 0 - 2mm | 2 - 4mm | > 4mm |
Torquing
This is one of the most difficult movements to achieve in orthodontics, both in traditional wire-and-bracket bracers and clear aligners. It is the movement of the tooth buccal or lingual with the CRot in the centre of the tooth, whereby the crown and root moves in opposite directions.
Torquing | Simple | Moderate | Difficult |
Anterior | 0 - 10o | 10 - 15o | > 15o |
Posterior | 0 - 5o | 5 - 10o | > 10o |
Intrusion
This is moving the tooth away from the occlusal plane and into the supporting periodontal structures. Molar intrusion is much more difficult to achieve in clear aligner treatment than incisor intrusion.
Intrusion | Simple | Moderate | Difficult |
Anterior | 0 - 1mm | 1 - 2mm | > 2mm |
Posterior | 0 - 0.5mm | 0.5 - 1mm | > 1mm |
Extrusion
This is moving the tooth toward the occlusal plane and out of the supporting periodontal structures. It is one of the most difficult movements to achieve in clear aligner treatment.
Extrusion | Simple | Moderate | Difficult |
Anterior | NA | 0 - 0.5mm | > 0.5mm |
Posterior | NA | 0 - 0.5mm | > 0.5mm |
Expansion (Moderate/Difficult)
This is the movement of teeth outward away from the midline and are moving in the ovular process. There are two different types of expansion, dental and skeletal.
Dental expansion is considered moderate to difficult movement with clear aligners.
Expansion (dental) | Simple | Moderate | Difficult |
| 0 - 2mm | 2 - 3mm | > 3mm |
Skeletal expansion is a difficult movement and generally not achievable in clear aligner treatment without an auxiliary appliance, such as a rapid palatal expander, to aid in the movement. Skeletal expansion is when the maxillary midline suture is opened, and true expansion of the maxillary bones occurs, providing for the outward movement and expansion. Typically, skeletal expansion is only attempted in young and growing patients.
Archform Constriction (moderate to difficult)
Archform constriction is moving the teeth inward towards the midline to reduce the size of the archform. It is a moderate to difficult movement in clear aligners.
Archform Constriction | Simple | Moderate | Difficult |
| 0 - 2mm | 2 - 3mm | > 3mm |
Malocclusions
Malocclusion | Simple | Moderate | Difficult |
Crowding | 0 – 3mm | 3 – 6mm | > 6 mm |
Spacing | 0 – 3mm | 3 – 6mm | > 6 mm |
Midline misalignment | 0 – 2mm | 2 – 4mm | > 4 mm |
Overjet | 0 – 2mm | 2 – 4mm | > 4 mm |
Overbite | 0 – 1mm | 1 – 3mm | > 3 mm |
Open bite | 0 – 0.5mm | 0.5 – 1mm | > 1 mm |
Other Conditions
Cases that have the following conditions can be difficult or impossible to treat with clear aligners:
Any type, method, or movement indicated as difficult
Centric-relation and centric-occlusion discrepancies
Teeth with short clinical crowns
Arches with multiple missing teeth
If the second molars have not yet erupted
Poor oral hygiene or active periodontal disease
Dental prosthetics or implants and/or
Severe bruxism
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